Connected: An Internet Encyclopedia
RFC 1321 - 5. Differences Between MD4 and MD5

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### 5. Differences Between MD4 and MD5

The following are the differences between MD4 and MD5:

1. A fourth round has been added.

2. Each step now has a unique additive constant.

3. The function g in round 2 was changed from (XY v XZ v YZ) to (XZ v Y not(Z)) to make g less symmetric.

4. Each step now adds in the result of the previous step. This promotes a faster "avalanche effect".

5. The order in which input words are accessed in rounds 2 and 3 is changed, to make these patterns less like each other.

6. The shift amounts in each round have been approximately optimized, to yield a faster "avalanche effect." The shifts in different rounds are distinct.

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Connected: An Internet Encyclopedia
RFC 1321 - 5. Differences Between MD4 and MD5